Vitamin K-dependent proteins (e.g., Factor IX) contain 9 to 13 gamma-carboxyglutamic acid residues (Gla) in their amino terminal 45 residues. The Gla residues are produced by enzymes in the liver that utilize vitamin K to carboxylate the side chains of glutamic acid residues in protein precursors. Vitamin K-dependent proteins are involved in a number of biological processes, of which the most well described is blood coagulation (reviewed in Nelsestuen, Vitam. Horm. 58: 355-389 (2000)). Vitamin K-dependent proteins include protein Z, protein S, prothrombin (Factor II), Factor X, Factor IX, protein C, Factor VII, Gas6, and matrix GLA protein. Factors VII, IX, X and II function in procoagulation processes while protein C, protein S and protein Z serve in anticoagulation roles. Gas6 is a growth arrest hormone encoded by growth arrest-specific gene 6 (gash) and is related to protein S. See, Manfioletti et al. Mol. Cell. Biol. 13: 4976-4985 (1993). Matrix GLA protein normally is found in bone and is critical to prevention of calcification of soft tissues in the circulation. Luo et al. Nature 386: 78-81 (1997).
The regulation of blood coagulation is a process that presents a number of leading health problems, including both the failure to form blood clots as well as thrombosis, the formation of unwanted blood clots. Agents that prevent unwanted clots are used in many situations and a variety of agents are available. Unfortunately, most current therapies have undesirable side effects. Orally administered anticoagulants such as Warfarin act by inhibiting the action of vitamin K in the liver, thereby preventing complete carboxylation of glutamic acid residues in the vitamin K-dependent proteins, resulting in a lowered concentration of active proteins in the circulatory system and reduced ability to form clots. Warfarin therapy is complicated by the competitive nature of the drug with its target. Fluctuations of dietary vitamin K can result in an over-dose or under-dose of warfarin. Fluctuations in coagulation activity are an undesirable outcome of this therapy.
Injected substances such as heparin, including low molecular weight heparin, also are commonly used anticoagulants. Again, these compounds are subject to overdose and must be carefully monitored.
A newer category of anticoagulants includes active-site modified vitamin K-dependent clotting factors such as factor VIIa and IXa. The active sites are blocked by serine protease inhibitors such as chloromethylketone derivatives of amino acids or short peptides. The active site-modified proteins retain the ability to form complexes with their respective cofactors, but are inactive, thereby producing no enzyme activity and preventing complexing of the cofactor with the respective active enzymes. In short, these proteins appear to offer the benefits of anticoagulation therapy without the adverse side effects of other anticoagulants. Active site modified factor Xa is another possible anticoagulant in this group. Its cofactor protein is factor Va. Active site modified activated protein C (APC) may also form an effective inhibitor of coagulation. See, Sorensen et al. J. Biol. Chem. 272: 11863-11868 (1997). Active site modified APC binds to factor Va and prevents factor Xa from binding.
A major inhibition to the use of vitamin K-dependent clotting factors is cost. Biosynthesis of vitamin K-dependent proteins is dependent on an intact glutamic acid carboxylation system, which is present in a small number of animal cell types. Overproduction of these proteins is limited by this enzyme system. Furthermore, the effective dose of these proteins is high. A common dosage is 1000 μg of peptide/kg body weight. See, Harker et al. 1997, supra.
Another phenomena that hampers the use of therapeutic peptides is the well known aspect of protein glycosylation is the relatively short in vivo half life exhibited by these peptides. Overall, the problem of short in vivo half life means that therapeutic glycopeptides must be administered frequently in high dosages, which ultimately translate to higher health care costs than might be necessary if a more efficient method for making longer lasting, more effective glycoprotein therapeutics was available.
Factor VIIa, for example, illustrates this problem. Factor VII and VIIa have circulation half-times of about 2-4 hours in the human. That is, within 2-4 hours, the concentration of the peptide in the serum is reduced by half. When Factor VIIa is used as a procoagulant to treat certain forms of hemophilia, the standard protocol is to inject VIIa every two hours and at high dosages (45 to 90 μg/kg body weight). See, Hedner et al., Transfus. Med. Rev. 7: 78-83 (1993)). Thus, use of these proteins as procoagulants or anticoagulants (in the case of factor VIIa) requires that the proteins be administered at frequent intervals and at high dosages.
One solution to the problem of providing cost effective glycopeptide therapeutics has been to provide peptides with longer in vivo half lives. For example, glycopeptide therapeutics with improved pharmacokinetic properties have been produced by attaching synthetic polymers to the peptide backbone. An exemplary polymer that has been conjugated to peptides is poly(ethylene glycol) (“PEG”). The use of PEG to derivatize peptide therapeutics has been demonstrated to reduce the immunogenicity of the peptides. For example, U.S. Pat. No. 4,179,337 (Davis et al.) discloses non-immunogenic polypeptides such as enzymes and peptide hormones coupled to polyethylene glycol (PEG) or polypropylene glycol. In addition to reduced immunogenicity, the clearance time in circulation is prolonged due to the increased size of the PEG-conjugate of the polypeptides in question.
The principal mode of attachment of PEG, and its derivatives, to peptides is a non-specific bonding through a peptide amino acid residue (see e.g., U.S. Pat. No. 4,088,538 U.S. Pat. No. 4,496,689, U.S. Pat. No. 4,414,147, U.S. Pat. No. 4,055,635, and PCT WO 87/00056). Another mode of attaching PEG to peptides is through the non-specific oxidation of glycosyl residues on a glycopeptide (see e.g., WO 94/05332).
In these non-specific methods, poly(ethyleneglycol) is added in a random, non-specific manner to reactive residues on a peptide backbone. Of course, random addition of PEG molecules has its drawbacks, including a lack of homogeneity of the final product, and the possibility for reduction in the biological or enzymatic activity of the peptide. Therefore, for the production of therapeutic peptides, a derivitization strategy that results in the formation of a specifically labeled, readily characterizable, essentially homogeneous product is superior. Such methods have been developed.
Specifically labeled, homogeneous peptide therapeutics can be produced in vitro through the action of enzymes. Unlike the typical non-specific methods for attaching a synthetic polymer or other label to a peptide, enzyme-based syntheses have the advantages of regioselectivity and stereoselectivity. Two principal classes of enzymes for use in the synthesis of labeled peptides are glycosyltransferases (e.g., sialyltransferases, oligosaccharyltransferases, N-acetylglucosaminyltransferases), and glycosidases. These enzymes can be used for the specific attachment of sugars which can be subsequently modified to comprise a therapeutic moiety. Alternatively, glycosyltransferases and modified glycosidases can be used to directly transfer modified sugars to a peptide backbone (see e.g., U.S. Pat. No. 6,399,336, and U.S. Patent Application Publications 20030040037, 20040132640, 20040137557, 20040126838, and 20040142856, each of which are incorporated by reference herein). Methods combining both chemical and enzymatic synthetic elements are also known (see e.g., Yamamoto et al. Carbohydr. Res. 305: 415-422 (1998) and U.S. Patent Application Publication 20040137557 which is incorporated herein by reference).
Factor IX is an extremely valuable therapeutic peptide. Although commercially available forms of Factor IX are in use today, these peptides can be improved by modifications that enhance the pharmacokinetics of the resulting isolated glycoprotein product. Thus, there remains a need in the art for longer lasting Factor IX peptides with improved effectiveness and better pharmacokinetics. Furthermore, to be effective for the largest number of individuals, it must be possible to produce, on an industrial scale, a Factor IX peptide with improved therapeutic pharmacokinetics that has a predictable, essentially homogeneous, structure which can be readily reproduced over, and over again.
Fortunately, Factor IX peptides with improved pharmacokinetics and methods for making them are described herein. In addition to Factor IX peptides with improved pharmacokinetics, the invention also provides industrially practical and cost effective methods for the production of these Factor IX peptides. The Factor IX peptides of the invention comprise modifying groups such as PEG moieties, therapeutic moieties, biomolecules and the like. The present invention therefore fulfills the need for Factor IX peptides with improved the therapeutic effectiveness and improved pharmacokinetics for the treatment of conditions and diseases wherein Factor IX provides effective therapy.